Method of prepregging with resin and novel prepregs produced by such method

Abstract

Disclosed is a process of forming a prepreg material having substantially no voids. According to the process of the invention, the reinforcing material is heated to a temperature above the temperature of the impregnating resin. The prepreg formed has substantially no voids and does not require lengthy consolidation when formed into useful articles.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a division of application Ser. No. 09 / 253,805, filed Feb. 19, 1999, now U.S. Pat. No. 6,524,690 which is a division of application Ser. No. 08 / 890,574, filed Jul. 9, 1997, now U.S. Pat. No. 5,911,932, each of which are hereby incorporated herein by reference.FIELD OF THE INVENTION[0002]The present invention relates to apparatus and method of prepregging materials such as fibers or other such reinforcements with resinous materials, especially with thermoplastic resin compositions. The invention further relates to prepregs produced by such apparatus or methods and to a method of using such prepregs to form articles having highly desirable properties.BACKGROUND AND SUMMARY OF THE INVENTION[0003]Reinforced thermoplastic and thermoset materials have wide application in, for example, the aerospace, automotive, industrial / chemical, and sporting goods industries. Thermosetting resins are impregnated into the reinforcing materi...

AI Technical Summary

Benefits of technology

[0003]Reinforced thermoplastic and thermoset materials have wide application in, for example, the aerospace, automotive, industrial / chemical, and sporting goods industries. Thermosetting resins are impregnated into the reinforcing material before curing, while the resinous materials are low in viscosity. Thermoplastic compositions are more difficult to impregnate into the reinforcing material because of comparatively higher viscosities. On the other hand, thermoplastic compositions offer a number of benefits over thermosetting compositions. For example, thermoplastic prepregs are easier to fabricate into articles. Another advantage is that thermoplastic articles formed from such prepregs may be recycled. In addition, a wide variety of properties may be achieved by proper selection of the thermoplastic matrix.

[0005]In the past, a thermoplastic composition has typically been heated, slurried, commingled, or diluted with solvents in order to reduce the viscosity of the composition before it is used to impregnate the reinforcing material. These methods have suffered from serious drawbacks. In the case of using solvent to reduce viscosity, the solvent must be driven off after the impregnation step, resulting in an additional step in the process as well as unwanted emissions. Moreover, the desired matrix may be insoluble in common solvents. In the case of heating the thermoplastic matrix in order to reduce its viscosity, the dwell time of the resin in the heated zone may result in degradation of the resin with attendant decrease in the desired mechanical properties. Furthermore, the molecular weight of the resin may need to be kept lower than would be desired for properties of the ultimate product in order to facilitate the impregnation step. Finally, as noted above, known processes for impregnating thermoplastic resin into reinforcing materials have required lengthy consolidation of the prepreg materials at high temperatures and pressures in order to develop the best physical strength and other properties and to minimize or eliminate outgassing during the consolidation or in later steps, e.g., finishing processes. Outgassing during consolidation results in voids within the composite that can cause microcracking or premature delaminiation that may adversely affect mechanical properties; outgassing during coating steps tends to cause pinholing or popping in the substrate or coating, resulting in an undesirably rough and blemished surfaces or finishes.

[0007]Because the length of time typically required to properly consolidate the prepreg plies determines the production rate for the part, it would be desirable to achieve the best consolidation in the shortest amount of time. Moreover, lower consolidation pressures or temperatures and shorter times will result in a less expensive production process, for instance due to lowered consumption of energy per piece for molding.

[0008]The present invention provides a new process for preparing prepregs, novel prepregs, and articles of reinforced materials that offers significant advantages over the processes described above. In the methods according the present invention, the reinforcing material is heated before being impregnated with the resinous matrix composition. The impregnated roving or tow that is produced according to the present inventive process has substantially no voids and can therefore be quickly and easily formed into a desired article having no voids or essentially no voids without the lengthy consolidation processes necessary for prepregs formed by other processes. In other words, the roving bundle is fully, or substantially fully, wet out. The only process that must take place in forming an article is fusion between impregnated bundles, and it is possible to use temperatures, pressures, and / or times during such forming operations that are significantly reduced over prior art processes.

Problems solved by technology

Thermoplastic compositions are more difficult to impregnate into the reinforcing material because of comparatively higher viscosities.

These methods have suffered from serious drawbacks.

In the case of using solvent to reduce viscosity, the solvent must be driven off after the impregnation step, resulting in an additional step in the process as well as unwanted emissions.

In the case of heating the thermoplastic matrix in order to reduce its viscosity, the dwell time of the resin in the heated zone may result in degradation of the resin with attendant decrease in the desired mechanical properties.

Outgassing during consolidation results in voids within the composite that can cause microcracking or premature delaminiation that may adversely affect mechanical properties; outgassing during coating steps tends to cause pinholing or popping in the substrate or coating, resulting in an undesirably rough and blemished surfaces or finishes.

However, the consolidation step still requires a dwell time under vacuum of up to sixty minutes or more.

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